Abstract: An understanding of eye development is necessary to comprehend proper functioning of the eye, capacity for regeneration, and the developmental basis of disease. Many model systems, both vertebrate and invertebrate, have historically provided much important data about the developmental and genetic basis of eye formation. However, hurdles exist studying eye development in model systems such as inherent biases in mutant screens and the minimal amount of naturally occurring variation in eye size. One novel approach allowing for a greater understanding of the developmental and genetic bases of eye formation is to examine naturally occurring eye size variation in non-model organisms, such as that occurs in cave animals. Our previous work demonstrated the utility of using non-model organisms to model human disease when we found that a commonly mutated gene in cases of human albinism was also responsible for albinism in the cavefish, Astyanax mexicanus. We initially chose the isopod crustacean, Asellus aquaticus as a model for studying eye variation because of the extreme difference in eye size between cave and surface dwelling populations. Our subsequent work on the species demonstrated further advantages including multiple independent mechanisms of eye reduction/ loss within a single cave population, multiple mechanisms of eye loss between different cave populations, and the large genetic component influencing eye size. We have already generated many molecular, developmental, and genetic tools and reagents that will assist in studying this interesting species. Our proposal aims to understand the genetics behind eye degeneration in this species. First, we use comparative transcriptome sequencing of cave and surface embryonic samples as an unbiased method to identify genes and pathways responsible for eye degeneration in the cave form. Second, we sequence transcriptomes of hybrid embryos to identify genes that show allele specific expression and that putatively contain cis-regulatory changes. Next, we validate genes discovered from the transcriptome sequencing using linkage and functional techniques. Our work provides a novel perspective on the developmental and genetic basis of eye size differences and furthers the development of A. aquaticus as an important model for eye degeneration and disease.